The developmental switch which occurs in hemoglobin production during embryonic, fetal and adult life serves as a model for studying the spatial and temporal specificity of gene expression. The K562 human erythroleukemia continuous cell line is a useful tool for examining globin gene expression as these cells express constitutively low amounts of embryonic and fetal hemoglobins and can be further induced for hemoglobin production by various chemical stimuli such as hemin. The structural requirements for active gene transcription are being assessed by examining the binding characteristics of nuclear protein extracts from K562 cells to regions of globin-DNA such as the epsilon promoter, using techniques such as gel-retardation electrophoresis, DNA- footprinting and ion exchange and affinity chromatography. To examine the functional requirements for transcription, a globin- hybrid gene system has been designed to facilitate the analysis, separation and recovery of viable cells in which the epsilon globin gene is activity transcribed.